Field of the Invention
The present invention relates to a splinter shield for a vacuum pump and a vacuum pump having the splinter shield. More particularly, the present invention relates to a splinter shield for a vacuum pump, which has a sufficiently enhanced fastening strength to a fixing groove and is capable of sufficiently preventing the splinter shield itself from bending toward the inside of a vacuum pump when air rushes into the pump through an inlet port, and further relates to a vacuum pump having such splinter shield.
Description of the Related Art
In a conventional high speed rotary vacuum pump such as a turbomolecular pump, a splinter shield for preventing the entry of foreign matters is mounted on an inlet port provided inside a flange part of a casing upper end part in order to prevent the entry of foreign matters to a rotator inside pump equipment through the inlet port. When the flange part is of ISO standards, the splinter shield cannot be screwed and fixed to the inlet port due to a space-related problem. In addition, without a predetermined strength, the splinter shield might bend toward the inside of the pump upon rush of air into the pump through the inlet port and come into contact with the equipment inside the pump, such as a rotary vane, causing damage to the pump. Therefore, the splinter shield needs to have a predetermined strength.
Under such circumstances, there exists a first conventional technology, shown in FIGS. 6 to 8A and 8B, for example, that has a splinter shield for a vacuum pump and a structure for fixing the splinter shield to an inlet port. FIG. 6 shows a wire net 1 with a circumferential edge rim 1a formed along a circumferential edge portion of the wire net. FIG. 7 shows a metal reinforcing plate 2 having a circumferential edge plate part 2a of a circumferential edge portion and a cross-shaped rib portion 2b disposed as a crosspiece within the circumferential edge plate part 2a. The splinter shield for a vacuum pump is obtained by superposing and appropriately spot-welding the wire net 1 and the reinforcing plate 2, which are formed separately, into an integrated composite part.
FIGS. 8A and 8B each show a structure for fixing the splinter shield 3, a composite part of the wire net 1 and the reinforcing plate 2, to an inlet port 4. An annular fixing groove 7 is provided in a concave manner inside a flange part 6 of an upper part of a casing 5 in the vacuum pump. The splinter shield 3 configured by the composite part described above has its superposed part, configured by the circumferential edge rim 1a and the circumferential edge plate part 2a, inserted in the fixing groove 7 and an annular retaining ring 8 pushed thereto. The splinter shield 3 is then fixed to the inlet port 4. The vacuum pump that is located immediately below the splinter shield 3 fixed to the inlet port 4 is equipped with a rotary vane 10 provided in a spread manner in a rotor 9 (FIG. 8A).
Further, FIG. 9 shows a second conventional technology that has a splinter shield for a vacuum pump and a structure for fixing the splinter shield to an inlet port. In this conventional technology, a splinter shield 11 for a vacuum pump is realized with a single part, and a brim part of the splinter shield 11 is tilted upward at a predetermined angle to form an inclined brim part 11a. A height h of the inclined brim part 11a corresponds to the insertion width of the fixing groove 7 (a vertical width in FIG. 9). Pushing this inclined brim part 11a into the fixing groove 7 without using a retaining ring can tightly couple the inclined brim part 11a and the fixing groove 7 to each other, thereby fixing the splinter shield 11 to the inlet port 4.
When air rushes into the pump through the inlet port 4, the inclined brim part 11a tends to deform in a manner shown by a virtual line in FIG. 9, wherein an upper edge part of the inclined brim part 11a comes into tight contact with an upper surface of the fixing groove 7, preventing the splinter shield 11 from falling and bending toward the inside of the pump.
For example, the following vacuum pump is known as a conventional technology relating to the vacuum pump described above. In this conventional technology, a casing base part is screwed and fixed to a lower flange part of a base configuring a substrate of a vacuum pump of turbomolecular pump type. A rotor is attached to an upper end of a rotating shaft of a casing central part. The rotor is provided with rotary vanes in a radially spread manner at certain intervals, the rotary vanes being directed toward an inner circumference of a casing. On the other hand, multiple steps of ring-shaped spacers are disposed in a stacked manner on the inner circumference side of the casing, and a stationary vane having its base part held between the spacers is provided in a manner as to extend toward the rotor. A turbo mechanism is configured by alternately superposing the rotary vanes and the stationary vanes from the inside and the outside. The splinter shield has an annular plate (ring) around the rim thereof so as to be mounted on an inlet port. This annular ring part is held between a step part of a casing upper part and the top spacer and then held by the inlet port (see Japanese Patent Application Publication No. H11-247790, for example).
The first conventional technology generates high costs because the splinter shield is formed with the composite part obtained by superposing the wire net and the reinforcing plate formed separately. In the structure for fixing the splinter shield to the inlet port, a flat section in which the circumferential edge rim of the wire net and the circumferential edge plate part of the reinforcing plate are superposed is inserted into the fixing groove, and then the retaining ring is pushed into the fixing groove. This easily results in inadequacy of fastening strength of the splinter shield to the fixing groove, and the splinter shield might bend more toward the inside of the pump, depending on the force of air rushing into the pump through the inlet port. Consequently, the splinter shield might come into contact with the equipment inside the pump, and the inserted part might be released from the fixing groove, dropping the splinter shield.
In the second conventional technology, the height h of the inclined brim part corresponds to the insertion width of the fixing groove, and pushing the inclined brim part into the fixing groove can tightly couple the inclined brim part and the fixing groove to each other and fix the splinter shield to the inlet port. Thus, it is difficult to manage the inclination angle and the height h of the inclined brim part, and it is extremely difficult to press the inclined brim part into the fixing groove to tightly couple the inclined brim part and the fixing groove to each other. In this regard, the second conventional technology generates high costs.
In the conventional technology described in Japanese Patent Application Publication No. H11-247790, multiple steps of ring-shaped spacers are disposed in a stacked manner on the inner circumference side of the casing, and the splinter shield is fixed to the inlet port by having the annular ring part between the top spacer and the step part of the casing upper part. Therefore, removing the splinter shield in order to replace the splinter shield requires a troublesome work of removing the screws fixing the casing based part to the lower flange part of the base.
A technical problem to be solved, therefore, is to reduce costs of a splinter shield by obtaining a single sheet of splinter shield having a required strength and enhanced fastening strength to a fixing groove, to prevent the splinter shield from bending toward the inside of a pump and coming into contact with equipment inside the pump when air rushes into the pump through an inlet port, so that the splinter shield does not fall, and to facilitate attachment and removal of the splinter shield with respect to the inlet port. An object of the present invention is to solve this problem.